The existence and use of ultrahard materials for forming tooling, cutting and/or wear elements is well known in the art. For example, polycrystalline diamond (PCD) is known to be used as cutting elements to machine and drill metals, rock, plastics and a variety of composite materials. Such known polycrystalline diamond materials have a microstructure characterized by a polycrystalline diamond matrix first phase, that generally occupies the highest volume percent in the microstructure and that has the greatest hardness, and one or more second phases, that generally consist of a solvent catalyst material used to facilitate the bonding together of diamond grains or crystals to form the polycrystalline matrix first phase during sintering.
PCD known in the art is formed by combining diamond grains (that will form the polycrystalline matrix first phase) with a suitable solvent catalyst material (that will form the second phase) to form a polycrystalline diamond body. The solvent catalyst material can be provided in the form of powder and mixed with the diamond grains or can be infiltrated into the diamond grains during high pressure/high temperature (HPHT) sintering. The PCD material is sintered at extremely high pressure/high temperature process conditions (e.g., 45 Kbar to 70 Kbar and 1300° C. to 1500° C.), during which time the catalyzing material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure (body).
Catalyzing materials used for forming conventional PCD include solvent metals from Group VIII of the Periodic table of elements, with cobalt (Co) being the most common. Conventional PCD can comprise from about 85 to 94% by volume diamond and a remaining amount being the solvent metal catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstices or interstitial regions that exist between the bonded together diamond grains and/or along the surfaces of the diamond crystals.
The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired. Many different Industries utilize such PCD materials for cutting, e.g., in the form of a cutting element, including automotive, oil and gas, aerospace, and mining to mention a few.
For use in the oil production industry, such PCD cutting elements such as shear cutters are configured for attachment to a subterranean drilling device, e.g., a fixed cutter drag bit. Thus, such PCD shear cutters are used as the cutting elements in fixed cutter bits that drill holes in the earth for oil and gas exploration. Such shear cutters generally comprise a PCD body that is joined to a substrate, e.g., a substrate that is formed from cemented tungsten carbide. The shear cutter is manufactured using an HPHT process that generally utilizes cobalt as a catalytic second phase material that facilitates sintering between diamond particles to form a single interconnected polycrystalline matrix of diamond with cobalt dispersed throughout the matrix.
The shear cutter is attached to the fixed cutter bit via the substrate, usually by a braze material, leaving the PCD body exposed as a cutting element to shear rock as the fixed cutter bit rotates. High forces are generated at the PCD/rock interface to shear the rock away. In addition, high temperatures are generated at this cutting interface, which shorten the cutting life of the PCD cutting edge. High temperature incurred during operation can cause the cobalt in the diamond matrix to thermally expand, wherein the cobalt has a higher coefficient of thermal expansion than that of the diamond, and wherein such thermal expansion mismatch may cause stresses and cracks to develop within the microstructure during use, thereby decreasing the performance service life of the PCD cutter. Further, the cobalt present in the in the PCD matrix may facilitate the conversion of diamond back to graphite at temperatures above 700° C., which will radically decrease the performance life of the cutting element.
Attempts in the art address the above-noted limitations have focused on the removal of the catalyzing material from the PCD body. In particular, such attempts have involved removing the catalyzing material from a portion of the diamond body or throughout the entire diamond body. While removing the catalyzing material from the PCD has reduced the unwanted effects of thermal mismatch and has improved thermal stability, resulting microstructure (comprising substantially the diamond matrix phase) lacks fracture toughness and strength. Thus, it is known in the art to infiltrate the treated PCD with materials capable of providing a closer thermal expansion match with the diamond, and/or that help to improve fracture toughness, and/or that do not promote the conversion of diamond to graphite during operation. Such described attempts have been useful in providing a PCD material having improved properties of thermal stability over conventional PCD.
However, certain end-use drilling applications call for PCD materials that not only have improved thermal stability, but also demonstrate improved properties of wear and abrasion resistance. Single-stage conventional HPHT processing produces a sintered PCD body having a maximum diamond volume fraction of 94 percent. The diamond volume fraction of a PCD material directly impacts the wear and abrasion resistance for such material, and thus the end-use performance and service life. While the above-described attempts, removing the catalyzing material from the PCD, have some impact of marginally improving the wear and abrasion resistance of the PCD material, the extent of such improvement ultimately is governed by the diamond volume content which remains unchanged.
It is, therefore, desired that PCD constructions and methods for making the same be developed in a manner that provides an improved degree of wear and abrasion resistance compared to conventional PCD materials. It is also desired that such PCD construction also be capable of providing improved thermal stability if so desired.